What exactly do you mean by a professional slideshow? A slideshow that must be shown at a business conference? If so, you shouldn't need any plug ins I can think of. Keynote or PowerPoint will suffice, just keep the animations to a minimum.
3D effect? Huh? Are you working from still photos, video, a mix of both? If you have no clue how to do it I'd think about starting with iMovie/iDVD. There are a ton of 3rd party transition effects for iMovie that have 3D-ish looks. iDVD has a couple of nice wedding themes built into it as well.
Maybe also look at this program - nice "Ken Burns-ish" effects - like iPhoto on steroids. In fact it's so tightly integrated that it feels like an Apple product. Boinx FotoMagico